A taxonomic review of the epiphyllous taxa of the genus Radula Dumort. in Thailand is presented, based on herbarium specimens and field surveys. Nine species are recognized, including two new records, R. nymanii Steph. and R. stenocalyx Mont. One new species, R. grandilobula Promma et Chantanaorr., is described and illustrated. The new species is characterized by the leaf-lobe subtriangular-ovate to falcate-ovate with a narrowly rounded to obtuse apex; the leaf-lobule falcate-ovate, upper half broadly extended, free margin recurved, apex strongly turning away from the stem; and the discoid gemmae occurring perpendicularly on ventral surface of leaf-lobes. A key to species, brief descriptions and illustrations are provided; ecology and geographical distribution of the species are also noted.